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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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package org.apache.cassandra.db.view;
import java.util.Optional;
import java.util.function.Predicate;
import com.google.common.collect.Iterables;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.dht.Token;
import org.apache.cassandra.locator.AbstractReplicationStrategy;
import org.apache.cassandra.locator.EndpointsForToken;
import org.apache.cassandra.locator.NetworkTopologyStrategy;
import org.apache.cassandra.locator.Replica;
import org.apache.cassandra.utils.FBUtilities;
public final class ViewUtils
{
private ViewUtils()
{
}
/**
* Calculate the natural endpoint for the view.
*
* The view natural endpoint is the endpoint which has the same cardinality as this node in the replication factor.
* The cardinality is the number at which this node would store a piece of data, given the change in replication
* factor. If the keyspace's replication strategy is a NetworkTopologyStrategy, we filter the ring to contain only
* nodes in the local datacenter when calculating cardinality.
*
* For example, if we have the following ring:
* {@code A, T1 -> B, T2 -> C, T3 -> A}
*
* For the token T1, at RF=1, A would be included, so A's cardinality for T1 is 1. For the token T1, at RF=2, B would
* be included, so B's cardinality for token T1 is 2. For token T3, at RF = 2, A would be included, so A's cardinality
* for T3 is 2.
*
* For a view whose base token is T1 and whose view token is T3, the pairings between the nodes would be:
* A writes to C (A's cardinality is 1 for T1, and C's cardinality is 1 for T3)
* B writes to A (B's cardinality is 2 for T1, and A's cardinality is 2 for T3)
* C writes to B (C's cardinality is 3 for T1, and B's cardinality is 3 for T3)
*
* @return Optional.empty() if this method is called using a base token which does not belong to this replica
*/
public static Optional getViewNaturalEndpoint(AbstractReplicationStrategy replicationStrategy, Token baseToken, Token viewToken)
{
String localDataCenter = DatabaseDescriptor.getEndpointSnitch().getLocalDatacenter();
EndpointsForToken naturalBaseReplicas = replicationStrategy.getNaturalReplicasForToken(baseToken);
EndpointsForToken naturalViewReplicas = replicationStrategy.getNaturalReplicasForToken(viewToken);
Optional localReplica = Iterables.tryFind(naturalViewReplicas, Replica::isSelf).toJavaUtil();
if (localReplica.isPresent())
return localReplica;
// We only select replicas from our own DC
// TODO: this is poor encapsulation, leaking implementation details of replication strategy
Predicate isLocalDC = r -> !(replicationStrategy instanceof NetworkTopologyStrategy)
|| DatabaseDescriptor.getEndpointSnitch().getDatacenter(r).equals(localDataCenter);
// We have to remove any endpoint which is shared between the base and the view, as it will select itself
// and throw off the counts otherwise.
EndpointsForToken baseReplicas = naturalBaseReplicas.filter(
r -> !naturalViewReplicas.endpoints().contains(r.endpoint()) && isLocalDC.test(r)
);
EndpointsForToken viewReplicas = naturalViewReplicas.filter(
r -> !naturalBaseReplicas.endpoints().contains(r.endpoint()) && isLocalDC.test(r)
);
// The replication strategy will be the same for the base and the view, as they must belong to the same keyspace.
// Since the same replication strategy is used, the same placement should be used and we should get the same
// number of replicas for all of the tokens in the ring.
assert baseReplicas.size() == viewReplicas.size() : "Replication strategy should have the same number of endpoints for the base and the view";
int baseIdx = -1;
for (int i=0; i
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